Gypsum products such as a dental model, an industrial model, and a wall-plastering material are sometimes appropriately colored according to their application. For example, the dental model (teeth model) can be prepared by pouring gypsum that is mixed with water into a female impression of teeth formed from a plastic material or the like to cure the gypsum, and then removing the impression of teeth (see, for example, Patent Literature 1 and Patent Literature 2). In preparing the dental model, a pigment is added to a powder of gypsum as a raw material to color the dental model to be obtained into a desired color.
In order to improve the colorability of a gypsum product to be obtained, such as a dental model, it usually becomes necessary to increase the amount of the pigment added to the gypsum. However, when the addition amount of the pigment is increased, it sometimes occurs that the cost required for coloration increases and the strength of the gypsum product to be obtained, which is a hardened body, is lowered.
Moreover, in the case where, for example, a colored gypsum hardened body such as a dental model is produced, gypsum that is mixed with water, when poured into an impression of teeth, is given mechanical vibration using a vibrator or the like. Thereby, the fluidity of the gypsum is secured and bubbles inside are removed. However, there has been a problem that, when the mechanical vibration is given to the gypsum that is mixed with water, the pigments aggregate to make color unevenness liable to occur in the gypsum hardened body to be obtained.